(1) Field of the Invention
This invention relates generally to DC-DC converters and relates more specifically to DC-to-DC converters in devices wherein a coil of an electric motor is used for an inductance required to convert a DC voltage.
(2) Description of the Prior Art
Electronic mobile devices are usually powered by DC sources such as batteries. A process that changes one DC voltage to a different DC voltage is called DC-to-DC conversion. Battery powered systems often stack batteries in series to achieve higher voltage. However, stacking batteries is not possible in many high voltage applications due to lack of space. Boost converters or step-up converters can increase the voltage and reduce the number of cells. A boost converter is a DC-to-DC converter with an output voltage greater than the source voltage. A boost converter is sometimes called a step-up converter since it “steps up” the source voltage. Since power must be conserved, the output current is lower than the source current.
Boost converters comprise usually an inductor to store energy from a DC-source as e.g. a battery, a switch, and a diode. The basic principle of a Boost converter consists in 2 distinct states. In the On-state, the switch is closed, resulting in an increase in the inductor current, in the Off-state, the switch is open and the only path offered to inductor current is through the diode D, the capacitor C and the load. This results in transferring the energy accumulated in the inductor during the On-state into the capacitor.
In regard of mobile electronic devices the challenge for the designer of such systems is to save space e.g. for the inductors required.
There are patents dealing with DC-to-DC converters:
U.S. Patent (U.S. Pat. No. 7,395,888 to Yamamoto et al.) teaches a vehicle drive device comprising an actuator located between an electric motor and axles for driving the vehicle, a built-in power source for supplying electric power to the actuator, and a control means for controlling the drive of the actuator. The built-in power source can be consisted of a battery, and the actuator can be consisted of an electromagnetic clutch. Here, the vehicle drive device further comprises a boost means, such as a DC-DC converter, for boosting voltage of the built-in power source such as the battery. The output voltage of the boost means is supplied electric power to the actuator such as the electromagnetic clutch. The output voltage of the boost means can be also supplied the electric power to the field coil of the electric motor.
U.S. Patent (U.S. Pat. No. 6,710,574 to Davis et al.) discloses a reversible DC motor drive including a DC/DC converter having a DC input, a first output having a first pulsed DC voltage and first DC voltage value, a second output having a second pulsed DC voltage and second DC voltage value, and a third output having a third pulsed DC voltage and third DC voltage value. The first and second outputs are adapted for electrical interconnection with armature terminals of a DC motor, and the third output is adapted for electrical interconnection with a field terminal of the motor. A microprocessor routine calculates motor speed from the motor armature voltage, field current and armature current. An outer control loop for motor speed and two separately controllable inner control loops for armature and field current control the DC/DC converter responsive to the calculated motor speed and a speed reference in order to independently control the three DC voltage values.
U.S. Patent (U.S. Pat. No. 7,368,899 to Chi) proposes a boost circuit including a DC/DC converter having a switch, receiving an input voltage and outputting an input voltage feedback signal, an output voltage feedback signal, an input current feedback signal and an output voltage after a boost of the input voltage, and a feedback control circuit having a pulse-width modulation limiting controller, coupled to the converter, receiving the input voltage feedback signal, the output voltage feedback signal and the input current feedback signal and generating an output signal with a fixed time period. The output signal is employed to control the switching of the switch so as to generate the boost.